Parallels Tempering Valve Advice

BigRob

My Powers LHMM434-1 tempering valve was oversized by 4 sizes and the thermal actuator seems to be shot. The factory helped me troubleshoot it and they were very helpful. The LHMM431-1 valve body doesn't work with the 434-1 check stops, so that is a bummer that requires me to remove everything. Before the Powers 434 the building had a MX128 that worked well for over 10 years. It was changed when we had a new tank installed because San Francisco hasn't allowed lead fittings for a while now. I called Honeywell and they say there are no plans to make the MX128 lead free.



I'm considering putting two Honeywell AMX102-UT-1LF's in parallel. Thoughts? Should I reverse return them or stage them with a pressure reducing valve?



I came up with 113 fixture units for our building using an online guide. 7 units have 2 full baths with tubs w/overhead showers. Five units have 2.5 baths with tubs w/overhead showers. All 12 units have dishwashers and laundry. 113 fixtures units is around 33-38gpm based on some stuff I found online. Using the powers web tool with the apartment/multifamily option and adding 12 laundry units I get 29gpm.



Has anyone created a manifold to favor one valve without using a bypass pressure valve? I will add isolation valve, too. I suspect the AMX will be around for a while.



The real X factor for me is determining the max pressure drop across the valves. The valves are on the roof of a three story building. The static pressure at the valves will be 45psig. Do I need to add pressure created by gravity as the water flows down to fixtures? How do I calculate the pressure drop completely?

Mark Eatherton

Pipe them parallel reverse return...

And you should be fine. Also, put in good isolation for each valve so you can shut one down to rebuild it while the other one stays online.



ME

BigRob

Thanks, ME

What do you think about the pressure drop situation?  Based on some other feedback, I'm assuming the procedure for sizing is to:



1) determine max GPM needed

2) determine min pressure for fixtures

3) estimate dynamic head losses

3) Find Cv that places max GPM pressure drop + dynamic head losses at min fixture pressure

4) Find best valve that meets Cv requirement



I am assuming that I need to use the 45psi at the valve to start with, so I should target a minimum pressure of around 25psi.  I see that 20psi is the minimum for showers.  Plus, I think I will gain some gravity pressure from the roof down to the fixtures.



What I don't have experience with is: when will people start to complain about low water pressure?  I'm also not certain if I should use the 45psi at the valve, or include the gravity pressure gains from the tempering valve to the fixtures.

Mark Eatherton

I think you'll be OK...

If you've taken all of the load parameters into consideration at the valve, I think you will be fine, there is a lot of flexibility. In fact, the IAPMO Green Plumbers council is completely reviewing and redoing the Hunters demand curves based on today's reduced flow rates. This will also affect drain sizing resulting in pipe size reductions on both sides of the demand.



In my minds eye, the difference in elevation should cancel each other out, just like water being circulated in a closed loop situation.



Worst case scenario, if the pipes in the system are extremely corroded (galvanized) you might have to set a small pressure boost station. I'd put that in your contractual proposal as a contingency caveat.



ME